#include <iostream>
#include <cstdint>
#include <cstdio>
#include <math.h>

using namespace std;

int main() {
    long double c;
    cin >> c;

    long double L = 0;
    long double R = abs(c);

    for (int i = 0; i < 200; ++i) {
        long double mid = L + (R - L) / 2;
        if (mid * mid + sqrt(mid) >= c) {
            R = mid;
        } else {
            L = mid;
        }
    }

    cout.precision(6);
    cout << R << endl;

    return 0;
}